Hybrid vehicles are driven by multiple powerplants including, but not limited to an internal combustion engine and an electric machine. The electric machine functions as a motor/generator. In a generator mode, the electric machine is driven by the engine to generate electrical energy used to power electrical loads or charge batteries. In a motor mode, the electric machine supplements the engine, providing drive torque to drive the vehicle drivetrain.
Improved fuel economy (FE) and ecological sentiment are motivating factors for hybrid vehicle purchase. Traditionally, hybrid manufacturers provide a labeled FE ratings including city and highway FE ratings. Although the label FE, as well as real-world fuel economy, of hybrid vehicles is usually higher than those of their non-hybrid counterparts, hybrid vehicles have been criticized for lower than expected FE.